About TIP122:

The TIP122 NPN Darlington transistor is a Darlington pair NPN transistor. It functions like a normal NPN transistor, but since it has a Darlington pair inside it has a good collector current rating of about 5A and a gain of about 1000. It can also withstand about 100V across its collector- Emitter hence can be used to drive heavy loads. The Darlington pair inside this transistor is shown clearly as its internal circuit schematic below

 TIP122 Darlington NPN Transistor internal connection circuit

As you can see, there are two transistors inside this TO-220 package in which the emitter of the first transistor is connected with the base of the second transistor and the collector of both transistors are connected together to form a Darlington pair. This increases the current gain and current rating of this transistor.

Pin Configuration:

 Number NameDescription
1BaseControls the biasing of transistor, Used to turn ON or OFF the transistor
2CollectorCurrent flows in through collector, normally connected to load
3EmitterCurrent Drains out through emitter, normally connected to ground


Features of TIP122 NPN Darlington transistor:

  • Darlington Medium-power NPN Transistor
  • High DC Current Gain (hFE), typically 1000
  • Continuous Collector current (IC) is 5A
  • Collector-Emitter voltage (VCE) is 100 V
  • Collector-Base voltage (VCB) is 100V
  • Emitter Base Voltage (VBE) is 5V
  • Base Current(IB) is 120mA
  • Available in To-220 Package

Where to TIP122:

This transistor is known for its high current gain (hfe = 1000) and high collector current (IC =5A) hence it is normally use to control loads with high current or in applications where high amplification is require. This transistor has a low Base-Emitter Voltage of the only 5V hence can  easily control by a Logic device like microcontrollers. Although care has to be taken to check if the logic device can source up to 120mA.

So, if you looking for a transistor that could be easily controlled by a Logic device to switch high power loads or to amplify high current then this Transistor might be an ideal choice for your application.

How to use TIP122:

Although TIP has high collector current and current gain, it is fairly simple to control the device since it has an Emitter-Base voltage (VBE) of only 5V and base current of only 120mA. In the below circuit I have used the TIP122 to control a 48V motor which has a continuous current of about 3A.

Circuit using TIP122 Darlington NPN Transistor


  • Can use to switch high current (upto 5A) loads
  • Can use as medium Power switches
  • Use where high amplification is needed
  • Speed control of Motors
  • Inverter and other rectifier circuits



2D dimensions will help you in placing this component at the time of making circuit on perf board or a PCB.

 TIP122 Darlington NPN Transistor 2D model


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